This invention relates generally to centrifugal compressors. More particularly, but not by way of limitation, this invention relates to a diffuser for a centrifugal compressor that includes a plurality of ribs located in a diffuser passageway.
In any centrifugal compressor as the fluid flow exits the impeller, the flow distribution is distorted. Specifically, such distorted flow is characterized by a low angle (relative to a tangent to the impeller circumference) fluid flow exiting most prominently adjacent to the shroud side of the diffuser. In the past, this distorted flow has been shown to cause severe compressor preformance problems.
In an attempt to alleviate the foregoing, vanes or ribs have been located in the diffuser passageways, as clearly shown in U.S. Pat. No. 4,395,197 issued July 26, 1983 to Yoshinaga et al and in U.S. Pat. No. 4,421,457 issued Dec. 20, 1983 to Yoshinaga et al. It will be noted in those patents that ribs, as distinguished from vanes, have been located in the diffuser passageways. (Ribs do not extend entirely across the passageway. Vanes do.)
It will also be noted in those patents that the leading edges of the ribs are located extremely close to the outlet or outer diameter of the impeller. Accordingly, such ribs are subjected to the shock loading and pounding resulting from pressure fluctuations created as the impeller blades move past the ribs. Such pressure is imposed on both the ribs and impeller blades. It is believed that such pounding may, therefore, result in fatigue of the ribs and of the blades, significant noise levels, and increased flow disturbance.
It should also be pointed out, however, that locating the ribs in this manner can aid in increasing the flow angle adjacent to the shroud side of the diffuser and thus increases the efficiency of the compressors in which they are located. However, the primary effect of the ribs is to redirect the low angle flow immediately adjacent to them, but will not redirect the low angle flow at all positions between adjacent ribs particularly at radii near the diffuser inlet. This creates the potential for reverse flow into the impeller with resulting performance degradation.
In FIGS. 7 and 7A of the '457 patent, there is also illustrated a tapered diffuser passageway that is provided with diffuser ribs. The tapered diffuser passageway, as illustrated therein, is of uniform taper starting with the largest dimension adjacent to the impeller outlet and tapering inwardly to the diffuser outlet.
An object of this invention is to provide an improved diffuser for centrifugal compressors that increases the efficiency of the compressors by providing a more uniform flow through the diffuser and incorporates features that substantially reduce the buffeting, noise, and shock loading of the diffuser ribs and of the impeller blades.